For numerous applications of X/γ rays, including dual energy/multi-energy CT and radiotherapy, it is an important requirement and prerequisite for these applications to acquire accurate energy spectrum information. Theoretically, an energy spectrum can be acquired by threshold scanning with a detector. A process of acquiring the energy spectrum may be briefly described as follows: (1) defining minimum energy of photons counted by the detector through a voltage value set by a digital-to-analog converter, to count incident photons with energy above the minimum energy; (2) consecutively changing the set voltage value, to acquire photon information corresponding to a plurality of energy thresholds; (3) differentiating data of the photon information, to acquire relative photon information between two adjacent energy thresholds of various energy thresholds, i.e., the energy spectrum. However, in practice, the energy spectrum acquired in the above process is seriously distorted as a response of the detector to the incident photons is not ideal. For different types of detectors, responses of the detectors to photons have different characteristics. For example, for a cadmium-telluride-cadmium/cadmium telluride detector, which is commonly used as a detector for counting photons, a distortion of a response of the detector to incident photons is mainly caused by a charge sharing effect, an escape phenomenon, a crosstalk phenomenon etc. Under the combined action of these effects, it is difficult to acquire an energy spectrum without distortion in practical applications.
In order to solve this problem, in an existing method, an estimated energy spectrum is acquired by implementing fine-tuning on an empirical equation using experimental data. In another existing method, the Monte Carlo method is used to implement fine modeling on a detection system, simulate a process of acquiring an energy spectrum, and estimate an actual energy spectrum according to a result of the simulation. However, the methods for estimating an energy spectrum either have limited accuracy or require complex modeling, and thus are subject to various limitations in practical use.